[requests] Add missing attributes and __init__ to JSONDecodeError stub

requests.exceptions.JSONDecodeError inherits from both InvalidJSONError
(via RequestException) and json.JSONDecodeError. Its custom __init__
explicitly calls CompatJSONDecodeError.__init__(msg, doc, pos) first,
which sets the json.JSONDecodeError instance attributes (doc, pos,
lineno, colno, msg).

However, due to the complex MRO, type checkers may not resolve these
inherited attributes correctly on the requests.JSONDecodeError class.
Explicitly re-declaring them ensures tools like mypy correctly recognize
attributes such as exc.doc when catching requests.JSONDecodeError.

Also adds the proper __init__ signature matching the runtime behavior.

Fixes #15167

Author: sedat4ras

stubs/requests/requests/exceptions.pyi

@@ -14,7 +14,17 @@ class RequestException(OSError):
     ) -> None: ...
 
 class InvalidJSONError(RequestException): ...
-class JSONDecodeError(InvalidJSONError, CompatJSONDecodeError): ...
+
+class JSONDecodeError(InvalidJSONError, CompatJSONDecodeError):
+    # requests.JSONDecodeError.__init__ explicitly calls CompatJSONDecodeError.__init__(msg, doc, pos),
+    # so these attributes from json.JSONDecodeError are always present on instances.
+    # Re-declared here to help type checkers resolve them despite the complex MRO.
+    msg: str
+    doc: str
+    pos: int
+    lineno: int
+    colno: int
+    def __init__(self, msg: str, doc: str, pos: int) -> None: ...
 
 class HTTPError(RequestException):
     request: Request | PreparedRequest | Any